The present invention relates to a novel antenna support mechanism for a polar mounted antenna which is especially useful in tracking communications satellites.
The satellites are placed in orbits about the earth for the purpose of facilitating earth communications. Communication satellites in geostationary orbits are generally placed in an equatorial initial geostationary orbit. Such communication satellites are constantly subjected to the gravitational forces exerted by the sun, moon, and the earth. In addition, the sun produces a radiation force which strikes such communication satellites. All these forces tend to cause a communication satellite to drift away from its equatorial position.
Most geostationary communication satellites are allowed to wander 0.1 degrees in the North/South direction and 0.05 degrees in the East/West direction from assigned longitudinal positions over the earth's equator. Thrusters on such satellites are used periodically to confine satellites to these limits. In actuality, the satellite appears to follow a figure eight track as viewed from the surface of the earth. It has been found that it takes relatively little fuel in the satellite thrusters to correct for East/West drift when compared to North/South drift. Thus, inclined orbit satellites are permitted to drift a larger distance in the North/South direction, as much as 8 degrees north or south. In addition, satellites tend to gradually change their inclination angle relative to the equator.
Earth-bound satellite antennas must consequently track movements of the inclined orbit satellites in order to receive usable signals.
Some dish antennas are supported by an azimuth over elevation mount system. These systems include motorized movement on the elevation axis or on the elevation and azimuth axes. It has been found that the azimuth over elevation mount is not entirely accurate and tends to receive signals from more than one satellite at a time, requiring frequency screening.
Preferably, satellite tracking antennas utilize a polar mount or modified polar mount. In the latter case, the antenna axis mount is inclined a fraction of a degree (toward the equator) from being parallel to the polar axis of the earth. Unfortunately, this type of mount has a problem tracking inclined orbit satellites which are found east or west of a true south direction. A satellite dish tends to skew in this regard. Prior art antenna support mechanisms have included a preset declination value, relative to the polar axis. Such declination adjustment greatly increases the accuracy of a satellite tracking antenna.
A polar mounted antenna support mechanism which possesses a declination tracking or adjustment mechanism which is easily motorized would be a notable advance in the communications field.